Exception in thread "main" java.lang.ErrorDo not use jtrexp.setLayout() use jtrexp.setLayout().getContentPane().setLayout() instead
at javax.swing.JFrame.createRootPaneException(JFrame.java.406)
at javax.swing.JFrame.setLayout(JFrame.java.472)
at jtrexp.<init>(jtrexp.java.13)
at jtrexp.main(jtrexp.java.54)